Requirements concerning wearing courses of airfield pavements are defined as follows (namely, in the regulations of the U. S. Federal Aviation Agency (FAA) Advisory Circular AC No. 150/5370-10B):
• Be impermeable to water and suitably protect intermediate course.
• Provide surface free of foreign object damage (FOD) (i. e., loose particles).
• Resist loads from aircrafts.
• Be smooth, with uniform surface.
• Maintain required antiskid properties.
• In specific areas should be resistant to spillage of fuel, hydraulic and deicing fluids, or other solvents.
Guidelines on specifications for pavements on civil installations are contained in
International Standards and Recommended Practices, AERODROMES. Annex 14 to the Convention on International Civil Aviation, Volume I—Aerodrome Design and Operations by the International Civil Aviation Organization (ICAO). The ICAO regulations regarding civil aerodromes mainly define the features of pavements affecting air traffic safety—minimum level of friction, sufficient smoothness, lack of presence of any loose particles (i. e., FOD) or grains bigger than 3 mm resting on the pavement.
The rules of the FAA and ICAO govern the methods and frequencies of testing the friction and macrotexture. Methods of permanent measurement of the friction factor described in both documents will not be referred to here. Measurements of macrotexture are usually carried out either with calibrated sand (sand patch test) or with the application of special greases (NASA grease smear method). The minimum surface texture depth recommended by the ICAO is 1.0 mm. It is worth noting here that the essential task of macrotexture is to enable water discharge from the pavement so that a layer of water does not build up between a wet runway and an aircraft’s tire (hydroplaning).
Bearing in mind that a newly paved, ungritted SMA layer is marked by a high degree of slipperiness, some problems with achieving the intended level of friction may develop. On the other hand, gritting, even when followed by sweeping with mechanical brooms to remove unbonded grains, gives rise to a real threat to airplanes due to FOD; thus gritting has generally been ruled out. So the proper level of friction to be obtained by an adequate grain size distribution and the application of coarse aggregate with a high polished stone value (PSV) index.
Requirements for asphalt mixes for airfields mainly comply with specifications for highway engineering in some countries; however in other countries, special technical requirements have been drawn up specifically for airfields. They differ from those for highway applications. But, in each case the ICAO specifications for the finished pavement should be satisfied.
One should also remember that binders applied to specified parts of airfield pavements should be checked for resistance to fuel and deicers because of the destructive actions of these substances. Some manufacturers of road binders offer special products for such applications. Also some research has been done in this area (Steernberg et al., 2000). The following two documents in a series of European Standards established adequate methods of testing:
• EN 12697-41, Asphalt Mixtures—Test Methods for Hot Mix Asphalt—Part 41: Resistance to Deicing Fluids
• EN 12697-43, Asphalt Mixtures—Test Methods for Hot Mix Asphalt—Part 43: Resistance to Fuel
According to EN 13108-20, the aforementioned tests of resistance to deicing fluids and fuels are specifically applicable to SMA used on airfields.
